This invention relates to a low-fogging finish treatment for upholstery leather, particularly for leather used as upholstery in automobiles and aircraft. The basic method of the invention involves the use of a fatliquoring agent for finish-treating upholstery leathers which includes the use of a distilled oil of vegetable or animal origin that has less than 3 percent fatty acid components of less than 16 carbon atoms.
The present invention is directed to a method and product for finish-treating tanned leather to significantly lower the tendency of the leather to give off low molecular-weight trace components which condense and accumulate on clear glass and plastic surfaces such as windows, windshields, dashboard instrument covers and the like. This occurrence is known as "fogging", and is highly undesirable. Aside from the aesthetic objections to the presence of a milky white or translucent oily substance on the interior surfaces which must be removed, fogging impedes the vision of the driver, particularly at night when the driver is faced with lights from oncoming traffic reflecting off of the fogged windshield.
Also, dust and dirt brought into the vehicle interior by the ventilation system can bond to these fogging components, causing a further decrease in visibility.
Because of the various aesthetic and safety concerns relating to fogging, including those mentioned above, automobile companies have established standards, against which upholstery leather is measured to determine its tendency to give off elements which cause fogging.
All leather must be tanned before it is suitable for use as upholstery leather. Tanning removes fats and oils naturally in the hides and conditions the hides for the end use to which they will be put. Depending on the end use, tanning may enhance strength, suppleness, resilience or resistance to wear. Often, all of these characteristics must be present to some degree, and part of the tanning process includes determining how to treat the leather in order to obtain an appropriate balance between these and other similar characteristics.
Typically, finish steps are required to add back certain elements of the leather to achieve desirable results. Finish steps typically add back oils removed from the leather during tanning, which provide softness, suppleness and other desirable characteristics to the tanned leather. It is these elements added back during finish treating which cause fogging. This finish process is called "fatliquoring", and is used to impart the desired properties to the tanned leather. Fatliquors lubricate the leather fibers so that after the leather is dried its fibers are capable of sliding over each other, thus rendering the leather pliable, and increasing the tensile and tearing strength of the leather. Fatliquoring also enhances the physical appearance of the leather by minimizing the tendency of the leather to permanently crease as the leather is bent or folded. Ideally, bending or creasing the leather produces only minimal fine wrinkles.
Some prior art processes of fatliquoring tanned leather require that the leather be baked to drive off volatile substances contained in the oils, solvents and emulsifiers contained in the fatliquor. Other prior art processes involve the use of a selected amphiphilic copolymer as a substantially solventless fatliquor. See, U.S. Pat. No. 5,348,807 to Hodders.